Circulating fluids are required in the rotary drilling of formations containing hydrocarbons. These circulating fluids are referred to as drilling muds. There are two major types of emulsion drilling fluids or muds, generally identified as oil-in-water emulsions and water-in-oil emulsions, each having its particular requirements, advantages and problems. Water-in-oil emulsions (oil-mud) are preferred in many applications.
These oil-mud circulating fluids are pumped down the drill pipe and out into the wellbore through holes in the drill bit and back up the well in the annular space between the drill pipe and walls of the wellbore, carrying with it drill cuttings and the like that are then removed before recirculation. This mud performs a number of functions, including removing drill cuttings, lubricating and keeping the bit cool, providing flotation to help support the weight of the drill pipe and casing, coating the wellbore surface to prevent caving in and undesirable flow of fluids in or out of the wellbore, including drilling fluids, brine, and the like.
Obviously, the properties of and the composition of these drilling mud formulations are complex and variable, depending on the conditions involved and the results desired to required including reuse and recycling of mud formulations. One of the most important properties of these drilling muds and other drilling fluids is that they be thermally stable and do not present rheological and thixotropic problems under the conditions of drilling.
A major constituent of these oil based drilling muds are colloidal or gelling agents, normally organophilic clays. Large amounts of the clays are often required to obtain the desired thixotropic properties in the mud formulations. It is difficult to readily incorporate these large amounts of clays into formulations. It is an object of this invention to provide improved formulations using less of the clays without loss of the required thixotropic and thermal properties of the oil-mud formulations. It is a further object to provide improved oil-mud formulations not containing clays.
Most organophilic clays will not yield or swell in the low viscosity, low aromatic content mineral seal oils often used in drilling mud formulations. While heat of about 120.degree. to 160.degree. F. will aid in the swelling or activation of the clay particles, most on-site mud mixing facilities do not have the capability of heating the oil during the large volume initial oil-mud makeup. While high shear may also be used to provide heat through frictional forces, to aid the clay particles to swell, most mixing plants do not have high shear equipment, which is expensive initially and in energy requirements and time. Further, because of relatively low yield, higher concentrations of organophilic clays are often required. The excessive amounts required initially cause major problems after hole displacement because of subjection to, and subsequent yield of the organophilic clays, to high downhole temperatures. It is another objective of this invention to maximize the yield of organophilic clay in a short time, at low shear rates, and to obtain savings in both time and materials in oil based mud formulations.